When it is intended to measure a distance between desired regions, a method for performing the measurement by directly pressing measurement equipment such as a ruler or a tape measure against a measurement portion is generally used. When a distance between objects over a wide range is measured or when a measurement target is moving, however, it is difficult to perform measurement directly. For example, for ensuring riding comfort and safety for a train, a distance between right and left rails (track gauge) is measured at many portions on the rails and whether the distance is within a prescribed range is checked in some cases, but the measurement portions are large in number and in area, so that a working becomes troublesome and it takes a huge amount of time to measure the whole. Further, for example, when displacement in a height of the waist of a runner, that is, a distance between a ground surface and the waist is intended to be analyzed for checking a form in sports, etc., since a measurement target is moving, the measurement is difficult to be performed directly. Thus, it is desired to measure a distance of a desired target in a non-contact manner. As one of the methods for performing measurement in a non-contact manner, a technique for performing measurement while visually checking a measurement portion by using an image has been proposed.
PTL 1 described below discloses a technique that an image capturing device provided with two imaging units is used to create a three-dimensional model of an object from a pair of images having binocular disparity and compute a length between two points designated by a user, and it becomes possible to measure an actual length between the two points designated on an image.